Today we're going to talk about Fallacies 
of Vacuity. 
An argument suffers from a fallacy of 
vacuity when the argument doesn't make 
any progress, doesn't go anywhere. 
There are two general ways this can 
happen. 
One way an argument could suffer from a 
fallacy of vacuity is when it begs the 
question. 
That is to say, when, in order to believe 
the premises of the argument, or to 
believe that the premises imply the 
conclusion, we already need to believe 
the conclusion. 
Without already believing the conclusion, 
we're not going to believe that it's a 
successful argument. 
That's begging the question. 
That's one way an argument could suffer 
from a fallacy of acuity. 
Another way an argument could suffer from 
a fallacy of acuity is when the 
conclusion doesn't say anything 
substantive. 
When a conclusion just says, for 
instance, well, either it's raining or 
it's not, something completely 
uninformative like that, something that 
doesn't provide you with any information 
that you wouldn't have known 
independently of the argument. 
Those are the 2 general ways in which an 
argument can suffer from fallacy of 
acuity. 
We'll first talk about begging the 
question. 
Let me start off by giving you a really 
simple example of begging the question. 
It's an example that's so obvious, that 
probably none of you would be guilty of 
this fallacy. 
Suppose you're in a strange city, 
and you're walking around, trying to find 
a particular street. 
And so you go up to a stranger in that 
city, a normal seeming stranger. 
And you ask them for the directions to 
this street that you're trying to find. 
And they say, oh, that street. 
that street is three blocks north of 
here. 
And now you think, well, the stranger 
said that that street is three blocks 
north of here. 
That street is three blocks north of 
here. 
Maybe you believe that because the 
stranger said it. 
And then from those two premises you 
conclude So the stranger told the truth. 
Now let's look at that argument. 
That argument has something puzzling 
about it. 
Premise 1, premise 1, the stranger said, 
the street is 3 blocks north. 
[SOUND] Premise (2) The street is 3 
blocks north, 
[SOUND] where premise two is something 
you believe, because that's what the 
stranger told you. 
And from those two premises, you draw the 
conclusion, the stranger was telling the 
truth. 
Now, notice something funny about this 
argument? 
This argument actually is valid. 
There's no possible way for the two 
premises of the argument to be true, if 
the conclusion, number three, is false. 
If both premises are true then the 
conclusion has to be true. 
So the argument is valid. 
Furthermore, we can imagine a situation 
where the argument is sound, because both 
of the premises are true. 
Right? If you really are walking around a 
strange city, 
and the stranger tells you that the 
street you're looking for is 3 blocks 
north. 
And, in fact, that street is 3 blocks 
north. 
Then, both of the premises of the 
argument are true. 
And so the argument, in that event, would 
be sound. 
Nonetheless, 
the conclusion of this argument is not 
one that you ought to believe on the 
basis of these premises. 
Now look, you could have all sorts of 
good reasons for believing this 
conclusion, for believing that the 
stranger told the truth. 
For instance, maybe a friend of yours 
could vouch for the strangers 
reliability. 
Maybe the stranger has an excellent track 
record of telling the truth, and people 
could tell you about this track record, 
alright? There could be all sorts of 
reasons to believe that the stranger told 
the truth. 
But the point I'm making right now is 
that these two premises can't be a good 
reason to believe that the stranger told 
the truth, if your reason for believing 
the second premise is just that the 
stranger said that the street was three 
blocks north of here. 
Now why is that? Why can't these two 
premises be a good reason for you to 
believe that the stranger told the truth? 
In the situation in which your reason for 
believing the second premise is just the 
truth of the first premise. 
Here's why. 
Suppose the stranger tells you that the 
street is three blocks north of there. 
Well, why should you believe that the 
street is really three blocks north of 
there? 
Well, you should believe it, just in case 
you have a good reason to believe already 
that the stranger told the truth. 
In other words, if you don't already have 
a good reason to believe that the 
stranger told the truth, then you're not 
going to have a reason to believe the 
second premise of this argument on the 
basis of the fact that the stranger said 
that the street was three blocks north of 
there. 
Right? The stranger might have said it, 
but so what? If you don't have any reason 
to believe that the stranger told the 
truth. 
So, if you have a good reason to believe 
the second premise of this argument, that 
the street really is three blocks north 
of there, 
and your good reason has to do with the 
fact that the stranger said that the 
street was three blocks north of there, 
then that shows that you already have 
some reason to believe that the stranger 
told the truth. 
So, if you go and draw the conclussion, 
the stranger told the truth, that 
conclusion, is something that you must of 
already had a reason to believe. 
So this argument can't give you anymore 
reason to believe it than you already 
had. 
So that's why this argument can't give 
you a reason to believe its conclusion 
even in the case, where the argument is 
sound. 
It might be sound but it's still 
ineffective. 
And this particular kind of 
ineffectiveness is one example of what 
I'll call begging the question. 
The argument doesn't make any progress 
because in order to draw the conclusion 
You already have to be justified in 
believing the conclusion. 
In short, you don't learn anything from 
the argument, you can only draw the 
conclusion if you had a good reason for 
believing the conclusion already. 
Now as I said, that example of begging 
the question is so obvious, 
I doubt any of you would be guilty of it 
or would fall for it. 
But let's consider an example of begging 
the question that's close to something I 
actually heard on American television 
just a couple of months ago. 
A friend of American Presidential 
candidate Mitt Romney said in an 
interview that Mitt Romney was going to 
win the American presidential election. 
And his reasoning was that since Mitt 
Romney never fails in any of his 
projects, and since one of his biggest 
projects ever was to win the American 
presidential election, Romney was going 
to win the American presidential 
election. 
Now consider that argument, that argument 
actully was offered by some prominent 
person on American television. 
Premise one. 
[SOUND] Mitt Romney [SOUND] never fails 
[SOUND] in his projects. 
[SOUND] Premise 2, [SOUND] Romney's 
running for President. 
Conclusion, 
[SOUND] 
Romney will win [SOUND] the presidency. 
Now, once again, notice this argument is 
valid. 
If both of the premises are true, then 
the conclusion has to be true. 
Right, if it is indeed one of Romney's 
projects to win the presidency, and if 
indeed he never fails in his projects, 
then he will win the presidency. 
So the argument is valid. 
But, is it guilty of a fallacy of acuity? 
Well, in this particular case, yes. 
It begs the question and the reason it 
begs the question is because whatever 
reason you have for believing the first 
premise of the argument, Romney never 
fails in his projects. 
Whatever reason you have for believing 
that must include some reason you have 
for believing the conclusion that Romney 
will win the Presidency. 
Unless you already have a reason for 
believing that Romney will win the 
Presidency, you can't have a good reason 
for believing the first premise of the 
argument, that Romney never fails in his 
projects. 
So, even though this argument is valid if 
there's no possible way for the premeses 
to be true and the conclusion is false, 
nonetheless, the argument does beg the 
question and so is guilty of a fallacy of 
acuity. 
We've considered a couple examples of 
begging the question, but consider yet 
one more. 
Suppose I tell you That God laid down all 
of his divine commandments in this 
pamphlet right here. 
And you ask me why I believe that. 
And I say, well, because the pamphlet. 
Says that God laid down all of his divine 
commandments in this pamphlet right here. 
And of course, God would not have laid 
down his divine commandments in a 
pamphlet that wasn't wholly true. 
So, this pamphlet right here must be 
wholly true and so must be true, that God 
laid down all of his divine commandments 
in this pamphlet right here. 
Now that's an example of begging the 
question, that is simultaneously an 
appeal to authority. 
That particular argument suffers from 
both of the two fallacies that we've 
described in this lecture and the last. 
It is an unjustified appeal to authority, 
and it begs the question, and I want you 
to consider in the exercises that follow 
which arguments suffer from that same 
combination of faults.